David Cameron's promise to tackle human trafficking is said to be in disarray after an exodus of expert Home Office staff and the sidelining of the official in charge of the policy.

A former police officer – one of the most senior figures to have been involved in investigating trafficking, who requested anonymity for fear of repercussions – said: "One of the concerns is the lack of continuity of staff at the Home Office. The entire original team has gone."

Cameron has repeatedly stated that trafficking is a priority for the coalition; only last week immigration minister Damian Green told parliament: "The UK is a world leader in its anti-trafficking work, but that does not mean we should stand still." But the inter-ministerial group on human trafficking has met only once, while specific targets for tackling the issue no longer feature on the Home Office website.

The voluntary sector, meanwhile, claims that officials are refusing to set agendas on trafficking or provide detailed timescales for action.

The government was due to unveil its four-part strategy to disrupt trafficking in March, but sources say it will appear in June at the earliest.

Even the government's recent decision to endorse the EU directive on human trafficking has led to concerns among MPs, who fear that ministers will be unwilling to appoint an independent rapporteur who would investigate government policies on trafficking and tell parliament whether the UK is fulfilling its obligations.

There are also concerns over the treatment of victims after they have escaped from their abusers. Evidence suggests that such women are being classified as illegal immigrants rather than victims of a crime. The Poppy Project, widely acknowledged as the UK's leading organisation for trafficking victims, and which last week had its Home Office funding removed after eight years, said there had been four attempts at forced deportations of victims in the past three weeks, compared with two in the previous three years.

A Home Office spokesman said: "There has been no delay. The strategy will be published shortly. The government remains committed to working with our international partners and seeking the views of expert groups in the UK to tackle this awful crime."

Opting into the EU trafficking directive and a new border police command would help target organised criminals.

A Home Office source said the changes to personnel were a routine staff redeployment and rejected claims of a lack of expertise among officials. Anti-trafficking plans, he said, would appear on the Home Office website when the strategy was published.